An automatic variable speed motor and method of controlling the same

Abstract

The application discloses an automatic variable-speed motor and a control method thereof, which comprises a motor shell, a motor stator, a motor rotor, a rectifier transformer module and a contactor module. The motor stator is embedded with multiple groups of symmetrical three-phase power windings and a group of power generation windings; the terminals of the multiple groups of three-phase power windings are respectively connected to the normally open or normally closed contact points of the contactor module; the other ends of the normally open or normally closed contact points of the contactor module are connected to three-phase lead-out wires; the three-phase lead-out wires are connected to the output ends of a motor controller or directly connected to a three-phase power supply; the power generation windings are connected to the input ends of the rectifier transformer module; and the output ends of the rectifier transformer module are connected to the control ends of the contactor module. The number of turns of the power generation windings can be changed to adjust the output voltage of the power generation windings at different rotating speeds; the voltage output characteristics of the rectifier transformer module are set to control the contact point action of the contactor module, the series-parallel connection of the motor windings at different rotating speeds is realized, and the automatic variable-speed purpose is achieved.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of winding switching type variable-speed motors, and particularly relates to an automatic variable-speed motor and a control method thereof. BACKGROUND

[0002] The winding switching motor adopts multiple sets of windings, which can be switched into series connection or parallel connection according to a control signal, the windings are in series connection when the motor runs at low speed, and the windings are in parallel connection when the motor runs at high speed, so as to widen the speed range of the motor and increase the high-efficiency running area of the motor, which is a commonly used technical means in the industry. In such applications, the switching control of the windings has always been a technical difficulty.

[0003] An invention with the authorized publication number CN102010617332.6 discloses a stepless speed regulation method for a double-speed brushless DC motor for an electric vehicle, the current angle position signal sent by an electronic accelerator and the vehicle speed signal sent by a vehicle speed sensor are received by a controller to control the series and parallel switching of windings, and then to control the smooth switching of the double-speed brushless DC motor in low-speed and high-speed modes, so as to realize the seamless connection of the electric vehicle at low speed and high speed.

[0004] An invention with the authorized publication number CN102069727B and the invention name Speed regulation control system of double-speed motor for electric vehicle active power also controls the closing and opening of the first contactor, the second contactor and the third contactor by receiving the vehicle speed feedback signal sent by the vehicle speed sensor and the vehicle speed setting signal sent by the electronic accelerator, so as to realize the smooth switching of the motor at low speed and high speed.

[0005] An invention with the authorized publication number CN109367404A and the invention name Electric vehicle double-speed motor intelligent system discloses an electric vehicle double-speed motor intelligent system, which comprises motor UVW each phase A winding, B winding, brake system, motor controller, intelligent control system and motor winding series and parallel conversion switch. The motor winding is composed of A phase winding and B phase winding. The intelligent control system obtains the motor winding state, motor speed, voltage, current and other information through the motor controller, adopts the control strategy of the Schmidt trigger function module of the ECU central control system, completes the intelligent switching of the series and parallel connection of the motor winding, realizes the variable structure double-speed function of the motor, realizes the intelligent control process of the brake control function, improves the driving efficiency of the motor at low speed, has a small current working condition at low speed, reduces the power of the controller, saves the cost, improves the duty ratio of the voltage at low speed, the pulsation of the power output is small, reduces the instantaneous amplitude of the battery discharge, and prolongs the service life of the power supply.

[0006] The winding switching type motor needs to use a special controller or control system to realize the switching of the winding and the speed regulation of the motor, the controller also needs to collect a large number of signals to control the series and parallel switching of the two sets of windings, the winding switching switch is powered by the controller or externally connected to a power supply, which consumes additional battery energy and reduces the system efficiency, and makes the whole control system more complex and reduces the reliability. Especially for motors that do not need a special controller, such as asynchronous motors, an additional complex control system is needed when the winding switching operation is performed, which leads to inconvenience of use, a significant increase in cost and limits the application of winding switching technology. In addition, when the winding switching type motor is used as the main drive motor of an electric vehicle, the traditional method is to set a fixed speed as the speed point of winding switching. This switching method has a serious defect, that is, when the vehicle repeatedly accelerates and decelerates near a certain speed (such as urban road congestion conditions), the winding of the motor will be frequently switched, which seriously affects the service life and reliability of the contactor. SUMMARY

[0007] In view of the deficiencies in the prior art, the present application provides an automatic variable speed motor and an implementation method thereof, which can realize safe and reliable automatic switching of the motor winding and variable speed operation without a special controller and external power supply.

[0008] The present application achieves the above technical objects by the following technical means.

[0009] An automatic variable speed motor, characterized in that it comprises a motor housing, a motor stator, a motor rotor, a rectifier and transformer module, a contactor module and a motor controller; the motor stator is embedded with a plurality of symmetrical three-phase power windings and a power generation winding, the terminals of the plurality of symmetrical three-phase power windings are respectively connected to the normally open or normally closed contacts of the contactor module, the other end of the normally open or normally closed contacts of the contactor module is connected to a three-phase lead-out line, the three-phase lead-out line is connected to the output end of the motor controller, and the input end of the motor controller is connected to a power supply; the power generation winding is connected to the input end of the rectifier and transformer module, and the output end of the rectifier and transformer module is connected to the control end of the contactor module; the rectifier and transformer module has rectification and output voltage regulation functions, the alternating voltage generated by the power generation winding can be converted into direct current voltage through the rectifier and transformer module, and the voltage output characteristic of the rectifier and transformer module can be set as follows: when the input alternating voltage is greater than or equal to Ua, the rectifier and transformer module outputs a constant direct current voltage VD to supply power to the contactor module, when the input alternating voltage is less than Ua and greater than Ub, the rectifier and transformer module outputs a direct current voltage VD that is proportional to the input alternating voltage, and when the input alternating voltage is less than Ub, the rectifier and transformer module outputs a voltage of 0; the rectifier and transformer module supplies the output direct current voltage VD to the contactor to make the normally open or normally closed contacts of the contactor attract and open, thereby controlling the series and parallel switching of the plurality of symmetrical three-phase power windings of the motor, and realizing automatic variable speed of the motor. b b a The rectifier and transformer module supplies the output direct current voltage VD to the contactor to make the normally open or normally closed contacts of the contactor attract and open, thereby controlling the series and parallel switching of the plurality of symmetrical three-phase power windings of the motor, and realizing automatic variable speed of the motor. ​​

[0010] In the above scheme, there is a fixed relationship between the output voltage and rotational speed of the generator winding as follows: Therefore, by setting the number of turns N1 of the generator winding, the motor speed can be made n. a At that time, the AC voltage generated by the generator winding is U. a And when the rotational speed is greater than n a At that time, the output voltage of the generator winding is greater than U. a Therefore, when the motor speed n>n a At that time, the input voltage of the rectifier transformer module is greater than U. a The rectifier and transformer module outputs a constant DC voltage VD to the contactor module. The contactor module contacts actuate, causing the multiple sets of symmetrical three-phase power windings of the motor to connect in parallel, enabling the motor to operate in the high-speed range. Simultaneously, the speed point n for switching from high speed to low speed is set. b When the motor speed n <n b At that time, the output voltage of the generator winding is less than U. b When the output voltage of the rectifier transformer module is 0, the contacts of the contactor module return to their initial state, and the multiple sets of symmetrical three-phase power windings become connected in series, enabling the motor to operate in the low-speed range.

[0011] In the above scheme, n a Let n be the speed at which the low-speed region switches to the high-speed region, and nb be the speed at which the high-speed region switches to the low-speed region. a Greater than n b The difference between the two speeds can be set in the rectifier transformer module. By setting two speed switching points, frequent winding switching and potential damage to the contactor can be avoided when the motor accelerates or decelerates near a certain speed switching point. The logic relationship for automatic winding switching based on the motor speed n is as follows:

[0012] Motor acceleration 0 < n < n b The motor operates in the low-speed range, with the windings connected in series;

[0013] Motor acceleration n b <n<n a The motor operates in the low-speed range, with the windings connected in series;

[0014] Motor acceleration n>n a When the motor operates in the high-speed range, the windings are switched to parallel connection;

[0015] Motor reduction n>n a The motor continues to operate in the high-speed range, and the windings continue to be connected in parallel;

[0016] Motor reduction n a >n>n b The motor is still operating in the high-speed range, with the windings connected in parallel;

[0017] Motor speed n < n b The motor enters the low speed region, and the winding switches to series connection.

[0018] In the above scheme, the set of power generation windings embedded in the motor stator is a single-phase winding or a three-phase winding.

[0019] In the above scheme, the rectifier transformer module is an AC-DC voltage conversion module, and the relationship between its input voltage U and output voltage V is set as:

[0020] U > U a V = VD;

[0021] U < U b V = 0;

[0022] U b U < U < U a When U increases, V = 0; when U decreases, V = VD.

[0023] In the above scheme, the contactor module is a direct current voltage controlled contactor.

[0024] The implementation method of the automatic variable speed motor, the motor has two working modes of low speed and high speed region operation; in the low speed mode state: the output voltage of the rectifier transformer module is lower than the control voltage of the contactor module, the contactor module contact maintains the initial state, and the multiple sets of symmetric three-phase power windings are connected in series, and the motor operates in the low speed region; in the high speed mode state: the output voltage of the rectifier transformer module reaches the control voltage of the contactor module, the contactor module contact acts, the multiple sets of symmetric three-phase power windings change to parallel connection, and the motor realizes high speed region operation.

[0025] The above scheme includes the following steps:

[0026] After starting the motor, the motor speed increases:

[0027] When the motor speed n < na, the power generation voltage of the power generation winding is less than Ua, the output voltage of the rectifier transformer module is 0, the contactor module contact maintains the initial state, and the multiple sets of symmetric three-phase power windings are connected in series, and the motor operates in the low speed region;

[0028] When the motor speed n > na, the power generation voltage generated by the power generation winding is greater than Ua, the output voltage of the rectifier transformer module is VD, the contactor module contact acts, and the multiple sets of symmetric three-phase power windings change from series connection to parallel connection, and the motor realizes high speed region operation;

[0029] When the motor speed decreases:

[0030] When the motor speed decreases to n b < n < na The generated voltage Ub of the power generation winding b a The output voltage of the rectifier and transformer module is still VD, the motor winding is maintained in parallel connection, and the motor operates in the high speed region.

[0031] When the motor speed drops to n < n b The generated voltage Ub of the power generation winding, the output voltage of the rectifier and transformer module is 0, the contactor module contacts return to the initial state, and the plurality of symmetric three-phase power windings change from parallel connection to series connection, and the motor operates in the low speed region.

[0032] Compared with the prior art, the automatic variable speed motor has the beneficial effects and significant progress that:

[0033] 1. The automatic variable speed motor produces control power through the power generation winding embedded in the motor stator, directly controls the contactor module through the rectifier and transformer module, realizes automatic switching of the motor winding, does not need external controller and power supply, is suitable for any structure form of motor, widens the application range of the winding switching technology, and reduces the power loss of the control system.

[0034] 2. The automatic variable speed motor can realize automatic switching of the winding by using the motor body structure, does not depend on external controller, can be directly matched with various general controllers, or can work directly through the power supply without controller, reduces the requirement for the controller, and simplifies the operation.

[0035] 3. The automatic variable speed motor can realize different speed switching points by adjusting the number of turns of the power generation winding and setting the voltage output characteristics of the rectifier and transformer module, and avoids the adverse effects caused by switching at a single speed point.

[0036] 4. The automatic variable speed motor and the implementation method thereof have simple and reliable motor structure, convenient and efficient implementation method, and are easy to popularize.

[0037] 5. The number of turns of the power generation winding can be changed to adjust the output voltage of the power generation winding at different speeds, the voltage output characteristics of the rectifier and transformer module are set to control the contactor module contacts, the series-parallel connection of the motor winding at different speeds is realized, and the purpose of automatic speed change is achieved. The automatic variable speed motor can realize automatic switching and variable speed operation of the winding by the motor body, does not need a special switching controller, can be directly matched with various general controllers, or can be directly connected with the power supply to work, reduces the requirement for the controller, and widens the application range of the winding switching motor. BRIEF DESCRIPTION OF DRAWINGS

[0038] Figure 1 ​Fig. 1 is a schematic diagram of a motor structure of an automatic variable speed motor according to an embodiment of the present application;

[0039] Figure 2 Fig. 2 is a schematic diagram of a motor system structure of an automatic variable speed motor according to an embodiment of the present application;

[0040] Figure 3 Fig. 3 is a schematic diagram of a series connection of two groups of three-phase power windings of an automatic variable speed motor according to an embodiment of the present application;

[0041] Figure 4 Fig. 4 is a schematic diagram of a parallel connection of two groups of three-phase power windings of an automatic variable speed motor according to an embodiment of the present application;

[0042] Figure 5 Fig. 5 is a schematic diagram of a connection of a contactor module and three-phase power windings according to an embodiment of the present application; Figure 1

[0043] Figure 6 Fig. 6 is a schematic diagram of a connection of a contactor module and three-phase power windings according to an embodiment of the present application; Figure 2 .

[0044] Reference numerals:

[0045] 1 - motor housing, 2 - motor stator, 3 - motor rotor, 4 - rectifier transformer module, 5 - contactor module. DETAILED DESCRIPTION

[0046] Embodiments of the present application are described in detail below with reference to the attached drawings, which show by way of example, embodiments in which like numerals indicate like elements or elements having the same or similar function throughout the several views. The embodiments described below are exemplary and are intended to be illustrative of the present application, and are not to be construed as limiting the present application.

[0047] In the description of the present application, it is to be understood that the orientations or positional relationships indicated by the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "axial", "radial", "vertical", "horizontal", "inner", "outer", etc. are based on the orientations or positional relationships shown in the drawings, and are merely for the convenience of describing the present application and simplifying the description, and therefore cannot be understood as indicating or implying that the devices or elements indicated must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as limiting the present application. In addition, the terms "first", "second" are only for the purpose of description, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the technical features indicated. Therefore, the features defined as "first", "second" can explicitly or implicitly include one or more of the features. In the description of the present application, the meaning of "a plurality of" is two or more, unless otherwise specifically limited.

[0048] ​​In the present application, unless otherwise explicitly specified and limited, the terms "mounting", "connection", "connecting", "fixing" and the like should be understood in a broad sense, for example, can be fixed connection, can also be detachable connection, or integrally connected; can be mechanical connection, can also be electrical connection; can be directly connected, can also be indirectly connected through an intermediate medium, can be internal communication of two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0049] In combination with the accompanying Figures 1 to 4 The automatic variable speed motor and its implementation method, including motor shell 1, motor stator 2, motor rotor 3, rectifier transformer module 4, contactor module 5 and motor controller. The motor stator 2 is embedded with a plurality of symmetrical three-phase power windings and a single-phase power winding. The terminals of the plurality of three-phase power windings are respectively connected to the normally open or normally closed contacts of the contactor module 5. Specifically, each terminal is respectively connected to the normally open contact of the contactor or each terminal is respectively connected to the normally closed contact of the contactor. The other end of the normally open or normally closed contact of the contactor module 5 is connected to the three-phase lead-out line of the motor. The three-phase lead-out line of the motor is connected to the output end of the motor controller. The input end of the motor controller is connected to the power supply. The power winding is connected to the input end of the rectifier transformer module 4. The output end of the rectifier transformer module 4 is connected to the control end of the contactor module 5.

[0050] The motor three-phase power windings A, B and C are connected in star type. Each phase power winding is wound by two or more groups of identical windings and connected through a DC contactor module. When the motor is running in the low speed region, the two groups of windings are in series connection, as shown in Figure 3 At this time, the number of turns of the three-phase power winding is doubled in series connection, the motor back electromotive force is high, the motor output torque is large and the speed is low; when the motor is running in the high speed region, the two groups of windings are in parallel state, as shown in Figure 4 At this time, the number of turns of the three-phase power winding is half of that in series connection, the motor back electromotive force is low, and the motor can run at high speed.

[0051] In combination with the accompanying Figure 5 The contactor module is connected to the three-phase power winding Figure 1 From Figure 5The diagram shows the connection between the three-phase power windings and the three contactors. These three contactors are DC contactors, forming a contactor module. Each phase power winding consists of two identical sets of windings wound in parallel. When the motor is operating at low speed, the contactor module maintains its initial state: normally closed contacts are engaged, normally open contacts are disengaged, and the two sets of windings are in series. When the motor switches from low speed to high speed, the contactor module activates, the normally closed contacts disengage, and the normally open contacts engage, switching the two sets of windings from series to parallel. Similarly, when the motor switches from high speed to low speed, the contactor module activates, the normally closed contacts engage, and the normally open contacts disengage, switching the two sets of windings from parallel to series.

[0052] Combined with appendix Figure 6 This is for connecting the contactor module to the three-phase power winding. Figure 2 ,from Figure 6 The diagram shows the connection between the three-phase power winding and six contactors. These six contactors are DC contactors, forming a contactor module. Each phase power winding consists of four identical sets of windings wound in parallel. When the motor is operating at low speed, the contactor module maintains its initial state: normally closed contacts are engaged, normally open contacts are disengaged, and the four sets of windings form two series paths, each consisting of two sets of windings connected in series. When the motor switches from low speed to high speed, the contactor module activates, the normally closed contacts disengage, and the normally open contacts engage, resulting in the four sets of windings connected in parallel. Similarly, when the motor switches from high speed to low speed, the contactor module activates, the normally closed contacts engage, and the normally open contacts disengage, again forming two series paths, each consisting of two sets of windings connected in series.

[0053] Similarly, when each phase winding of the motor consists of 2N identical windings wound in parallel, where N>0 and N is an integer, the contactor module consists of 3N DC contactors. In the low-speed operating region, the normally closed contacts of the contactor module are engaged, and the normally open contacts are disengaged, resulting in N series paths for the 2N windings. Each series path consists of two windings connected in series. In the high-speed operating region, the normally closed contacts of the contactor module are disengaged, and the normally open contacts are engaged, resulting in the 2N windings connected in parallel.

[0054] After the motor starts, the motor speed is low. When the motor speed n <n a When, where n a To set the rotational speed, the voltage generated by the generator winding is low. The output voltage of the rectifier transformer module 4 is lower than the control voltage of the contactor module 5, so the contacts of contactor module 5 remain in their initial state. The multiple three-phase power windings of the motor are connected in series, and the motor operates in the low-speed range. At this time, adjusting the motor controller increases the motor speed. When the motor speed n > n aAt this time, the generated voltage from the generator winding is relatively high. This generated voltage, after passing through the rectifier transformer module 4, reaches the control voltage of the contactor module 5. The contactor module contacts 5 actuate, and the multiple three-phase power windings of the motor change from a series connection to a parallel connection, enabling the motor to operate in the high-speed range. Continue adjusting the motor controller to reduce the motor speed. When the motor speed decreases to n... a <n <n b During the interval, the rectifier transformer module detects the output voltage of the generator winding and outputs a corresponding voltage, controlling the winding to continue operating in parallel. When the motor speed drops to n... <n a When the generator winding produces a low voltage, the rectifier transformer module 4 outputs a voltage of 0, the contactor module 5 contacts return to their initial state, and the multiple power windings of the motor change from parallel connection to series connection, allowing the motor to operate in the low-speed range. This automatic high-low speed switching enables the motor to meet the speed requirements under different operating conditions.

[0055] Working principle of the invention:

[0056] The generated voltage from a set of generator windings embedded in the motor stator 2 is converted into DC voltage by the rectifier transformer module 4 to power the contactor module 5. The opening and closing of the normally open or normally closed contacts of the contactor module 5 controls the series and parallel switching of multiple three-phase power windings of the motor, enabling automatic speed regulation without an external power supply. According to the voltage formula of the motor generator windings: It can be known that the generating voltage E f Related to the motor speed n and the number of turns N1 of the generating winding, a suitable number of turns N1 is set so that when the speed reaches na, the DC voltage VD output by the rectifier transformer module 4 is such that if V d When the control voltage requirement of contactor module 5 is met, contactor module 5 actuates. Therefore, setting the generator turns N1 can control the motor speed n>n. a When the motor's multiple three-phase power windings are connected in parallel, the motor automatically switches to high-speed operation; when the motor speed n <n b When the output voltage of rectifier transformer module 4 is lower than the control voltage of contactor module 5, the contacts of contactor module 5 return to their initial state, and the multiple three-phase power windings of the motor become connected in series, enabling the motor to operate in the low-speed range. This method uses the generated voltage from the generator winding embedded in the motor stator to control the series-parallel switching of the multiple three-phase power windings of the motor, thereby controlling the high-speed and low-speed switching of the motor and achieving automatic speed change of the motor without the need for an external power supply and controller.

[0057] In the above embodiments, if the three-phase power winding of the motor is simplified to a single-phase power winding, the motor becomes a single-phase motor, and the same method can still be applied.

[0058] In the description of the specification, the description of the terms "one embodiment", "some embodiments", "an example", "a specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. In the specification, the illustrative description of the above terms does not necessarily mean the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0059] Although the embodiments of the present application have been shown and described above, it is understood that the above-described embodiments are exemplary, and should not be construed as limiting the present application, and those skilled in the art can make changes, modifications, replacements and variations to the above-described embodiments within the scope of the present application without departing from the principles and spirit of the present application.

Claims

1. An automatic variable speed motor characterized by, The motor includes a motor housing, a motor stator, a motor rotor, a rectifier transformer module and a contactor module. The motor stator is embedded with a plurality of symmetrical three-phase power windings and a power generation winding. Terminals of the plurality of symmetrical three-phase power windings are respectively connected to normally open or normally closed contacts of the contactor module. The normally open or normally closed contacts of the contactor module are connected to three-phase output lines. The three-phase output lines are connected to an output end of a motor controller or directly connected to a three-phase power source. The power generation winding is connected to an input end of the rectifier transformer module. An output end of the rectifier transformer module is connected to a control end of the contactor module. A power generation voltage generated by the power generation winding is converted into a direct current voltage by the rectifier transformer module to supply power to the contactor module. The contactor module controls the series-parallel connection of the plurality of symmetrical three-phase power windings by opening and closing of the normally open or normally closed contacts, thereby realizing automatic speed change of the motor. The number of turns of the power generation winding can be set to adjust the power generation voltage of the power generation winding at different rotational speeds. The rectifier transformer module can output a direct current voltage according to the input voltage of the power generation winding according to a certain rule. When the rotational speed is n a and n b , the output voltage of the power generation winding is U a and U b , respectively, and n a > n b , U a > U b . When the rotational speed of the motor is n a , the output voltage of the rectifier transformer module reaches the control voltage of the contactor module, the contactor module is actuated, the plurality of symmetrical three-phase power windings are connected in parallel, and the motor realizes high-speed operation. When the rotational speed of the motor is n b , the output voltage of the rectifier transformer module is lower than the control voltage of the contactor module, the contactor module returns to the initial state, the plurality of symmetrical three-phase power windings are connected in series, and the motor realizes low-speed operation.

2. The variable speed motor of claim 1, wherein, The embedded power generation winding group in the motor stator is a single-phase winding group or a three-phase winding group.

3. The variable speed motor of claim 1, wherein, The rectifier voltage transformation module is an AC-DC voltage transformation module, and the relationship between the input voltage U and the output voltage V is set as: U a V = VD when t = T U < U b V = 0 when t = 0. U b 〈U〈U a V = 0 when U is increasing; V = VD when U is decreasing, where the rotational speed n a The AC voltage value generated by the power generation winding is U a The AC voltage value generated by the power generation winding is U b The AC voltage value generated by the power generation winding is U b .

4. The variable speed motor of claim 1, wherein, The contactor module is a direct current voltage controlled contactor.

5. The control method of an automatic variable speed motor according to any one of claims 1 to 4, characterized in that, The switching of the motor winding from low speed to high speed and from high speed to low speed corresponds to different speed points n a and n b ; After starting, the motor is in an accelerating state, and the motor speed increases; When the motor speed n < n a , the power generation voltage of the power generation winding is less than U a , the output voltage of the rectifier transformer module is 0, the contactor module contact remains the initial state, the multiple sets of the symmetrical three-phase power winding are connected in series, and the motor runs in the low-speed region. When the motor speed n>n a , the generated voltage of the power generation winding is greater than U a , the rectifier voltage VD is output, the contactor module contacts are actuated, and the multiple sets of symmetric three-phase power windings are connected in series to parallel connection, and the motor realizes high-speed area operation. When decelerating, the motor speed decreases: When the motor speed drops to n b < n a , the generated voltage U b < U a of the generator winding is still VD, the motor winding maintains parallel connection, and the motor works in the high-speed region. When the motor speed drops to n < n b , the generated voltage U b of the power generation winding is 0, the output voltage of the rectifier transformer module is 0, the contactor module contacts return to the initial state, and the multiple sets of the symmetrical three-phase power windings change from parallel connection to series connection, and the motor runs in the low-speed region.

6. The control method of an automatic variable speed motor as set forth in claim 5, wherein The three-phase power winding group can be replaced by a single-phase power winding group or a power winding group with more than three phases, so that the motor becomes a single-phase motor or a multi-phase motor.

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